Southern California soon will begin sending sewage sludge into western Kings County -- up to 500,000 tons a year to a piece of farmland the size of Clovis.

It's the San Joaquin Valley's newest mega-composting project, mixing treated human waste from 5.7 million people and woody debris from area farming.

The compost will be used as soil nutrient on scrubby land at Westlake Farms to help grow cotton, wheat, pomegranates, pistachios and other crops.

But make no mistake about this enterprise. The Sanitation Districts of Los Angeles County -- serving 78 cities, including Long Beach and Beverly Hills -- bought 14,500 acres of farmland so there would be a place to send these pungent truckloads.

The first sludge, or biosolids, probably will arrive late next summer, the sanitation agency says.

The project's yuck factor lit up the Valley's west side 10 years ago when the L.A. districts bought the land. Distaste lingers today among environmentalists and residents of nearby Kettleman City.

But the $120 million project has survived appeals of its county operating permit, a lawsuit over air quality and continuous scrutiny.

The challenges have driven the L.A. districts to plan a cutting-edge project, including a biosolids-mixing building where the oxygen is literally sucked out and filtered for odors and air pollutants.

The L.A. districts spent $9 million on special fabric to trap ozone-making gases on huge composting piles.

"This is a top-notch, Cadillac system," said Ajay Malik, supervising engineer with the L.A. districts. "We have addressed the concerns about this project."

The project will be built in phases, the first of which will take about 100,000 tons of biosolids each year, Malik said. It will add to the several recycling options the L.A. districts have in Southern California and the Valley, including Kern County.

If necessary, the L.A. districts can expand to take 500,000 tons of biosolids and 400,000 tons of green waste. It would produce more than 300,000 tons of compost each year.

Environmentalists are not optimistic, though they settled their air-quality lawsuit over the project years ago. Activist groups and some Kettleman City residents worry about adding any waste to the area.

Known to some Kettleman City residents as "aqua negra" or black water, the sludge is just another contaminant being dumped on the area, activists say.

The town has arsenic and benzene contamination in the drinking water, diesel pollution from nearby Interstate 5, pesticides from farming and the West's largest toxic waste landfill nearby.

"We're watching this sewage sludge very closely," said Delano-based lawyer Caroline Farrell of the Center on Race, Poverty and the Environment, which filed the air-quality lawsuit against the composting project years ago.

But composting with treated human sewage has been going on for many years throughout the United States and the San Joaquin Valley. The federal government says the nutrient is safe to use in your backyard. On the ingredient label of some garden soil amendments, "biosolids" refers to sewage sludge.

The chunky, dark biosolids produced by sewage treatment still have bacteria, metals and some other impurities flushed down toilets and drains. But the biosolids are mixed with prunings and other green waste and left in a pile to decompose. Natural processes heat up the piles and kill bacteria.

Government regulations require monitoring to make sure the metals are at safe levels. Many millions of tons of biosolids have been trucked over the Tehachapi Mountains from Southern California into the Valley where they have been spread and used on crops, especially in Kern County.